1. Field of the Invention
The present invention relates to heart monitoring and non-surgical, automatic cardioverter/defibrillator devices.
2. Description of the Related Art
Sudden Cardiac Death (SCD) is the leading single cause of death in the United States today. SCD frequently results from the precipitous onset of electrical instability in the auto-nervous system which regulates the beating of the heart. This electrical instability may result in the development of catastrophic cardiac ventricular arrhythmia, which in most cases, if therapeutic or resuscitative measures are not taken immediately, can lead to serious injury or death.
Studies have shown that the most frequent arrhythmias recorded by emergency medical response teams are ventricular fibrillation (quivering of the heart) and ventricular tachycardia (dangerously fast heart rate). The conditions which indicate the onset of ventricular fibrillation and ventricular tachycardia include irregular and/or dangerously fast electrical impulses transmitted to the heart, and a lowering of the blood oxygenation level and blood pressure. Thus, it is possible to monitor these conditions in order to detect the onset of either ventricular fibrillation or ventricular tachycardia.
In addition to anti-arrhythmic drugs, therapeutic electrical devices are available for the management of such abnormal heart rhythms. For instance, implantable cardioverter/defibrillators (ICDs) are available to control ventricular tachyarrhythmias and fibrillation. These devices are implanted in a patient with electrodes attached directly to the heart. ICDs automatically sense the onset of life threatening arrhythmias and apply electrical energy pulses, which are synchronized with a detected heart beat during cardioversion to stabilize cardiac impulses produced by the auto-nervous system. This procedure for restoring normal heart functions is commonly known as cardioversion or defibrillation. Implantable pacemakers are also available, typically to provide bradycardia pacing of the heart when the heart rate is too slow.
ICDs are often implanted in persons who are known to suffer from recurring ventricular tachycardia and/or ventricular fibrillation, particularly when drug therapy is ineffective. Because ICDs are automatic and implanted in the patient, they allow a patient to remain ambulatory even when the patient may be at risk of ventricular tachycardia or ventricular fibrillation. Thus, ICD patients are often able to carry on a somewhat normal lifestyle. Otherwise, these patients are often confined by constant medical care requirements or they risk SCD. However, ICDs require surgery with many accompanying risks.
External, yet portable automatic defibrillator devices have also been proposed. For instance, U.S. Pat. No. 4,576,170 proposes a portable automatic defibrillator. However, a number of serious limitations have hampered the development of such devices, particularly ambulatory devices. For instance, a significant amount of signal noise and artifact are associated with externally monitoring the condition of a patient's heart beat. Thus, accurate analysis of the signals is difficult. This is often due to the movement and activity of the person wearing the device.
Because of the noise and artifacts present in external monitors, the state-of-the art heart monitoring devices may fail to accurately detect an abnormal or unsatisfactory cardiac rhythm. In addition, these monitoring devices could misinterpret the signal variations caused by noise and artifact as the onset of an abnormal condition, causing the defibrillator system to initiate unnecessary corrective therapy. The unnecessary initiation of therapy can create a state of electrical instability which may cause the onset of ventricular fibrillation, thereby placing the patient's life at risk.
A further limitation of existing and proposed devices is that they are limited in their adaptability from patient to patient. The devices have parameters predefined which generalize the detection of arrhythmias and the therapy administered